1. Field of the Invention
The present invention relates to an edge detection device, an image forming apparatus, and an edge detection method.
2. Description of the Related Art
For example, in image forming apparatuses for forming an image on a conveyance object such as a recording sheet, misregistration in a width direction (a direction orthogonal to a conveying direction) of the conveyance object leads to misregistration of the image. To solve this problem, an edge position in the width direction of the conveyance object is detected, and a position at which the image is formed is adjusted corresponding to a misregistration amount (main scanning registration error) between the detected edge position and a reference position in design.
For example, Japanese Patent No. 4794979 discloses a technique in which a contact image sensor (CIS) is arranged in a conveyance path of the conveyance object, an output from each photoelectric conversion element included in the CIS is binarized, and the edge position in the width direction of the conveyance object is detected from a binarized digital signal. The photoelectric conversion elements in the CIS are arranged to be aligned along the width direction of the conveyance object, and outputs from the photoelectric conversion elements are significantly different between a position overlapping with the conveyance object and a position not overlapping with the conveyance object. Thus, the position of the photoelectric conversion element at which a value of the binarized digital signal is switched can be detected as the edge position in the width direction of the conveyance object.
However, for the edge detection device in the related art that detects the edge position in the width direction of the conveyance object using the CIS, it is not assumed to use a conveyance object with a hole such as a conveyance object with a punch hole and a conveyance object with holes at some spots. Accordingly, when a conveyance object with a hole is being conveyed, an edge portion of the hole may be erroneously detected as the edge position in the width direction of the conveyance object, that is, detection accuracy for the edge position is insufficient.